When an injured photographer believes he?s witnessed a murder, he must overcome his limited mobility and cooperate with his girlfriend to bring the killer to justice.

I think describing the nature of his limited mobility would benefit the logline. Otherwise it's just another murder mystery, but what could make this interesting is the handicap the main character is forced to overcome in order to bring the killer to justice.

The greater the handicap the greater the challenge and the greater the challenge the more interesting the story.

After a [challenging mobility] photographer witnesses a murder he must enlist his girlfriend's help to bring the killer to justice.

On a side note, you could make it a comedy and make him need to enlist his mother's help or better yet his grandmother's help.